Flat Flywheel for LH2.4

OK...so my AW died a horrible death. Since I have a couple of M46's laying around and all the pieces from a donor car I figure now's the time. What I forgot was the 60-2 crank sensor wheel. After countless searches and an earlier post on the subject, here's what I did.

I took the flat, stock flywheel and reduced the diameter on a brake lathe just enough that the flexplate would slip over it with persuasion. Then, I laid the flexplate on top of the flywheel, both oriented the same and marked the "dead" spot. It's important that the flexplate and flywheel are both facing the same way and in line with the flexplates bolt holes. If they're facing each other, the location will be mirror imaged. I flipped the flexplate over and forced it over the edge of the flywheel with a rubber mallet. I clamped them together w/ 2 pairs of vise grips (over kill, but I wanted no chance of slipping). Drill press, 3/8in bit, 3/8 deep. I used the flexplate as my template and drilled 58 dimples into the side of the flywheel. Because the diameter of the flywheel had been reduced 3/32in, I had to grind the same amount off the bottem of the crank sensor bracket. Started first time!

Whoa...

Whoa nice! Great use of a brake lathe

Well, I called two different "CNC" metal shops locally that advertised automotive work. Neither one felt they could do it. The entire thing took about an hour, not counting the machining of the crank sensor mount.

I have two flat flywheels I'm not using and MikeP has a brake lathe...hmm.......

Heck, do it! When I searched and saw apparently no one had done this...well, I had nothing to lose. I googled pics of the dog bowls w/ sensors, and saw they apparently don't go thru...the rest was easy. I still can't get over two different so-called CNC machine shops wouldn't attempt this. I still need to balance it w/ the pressure plate on and test drive it...but it ran fine as you see it in the pic.

So no foot severances yet! fingers crossed. Pardon my ignorance, I know I should know this, but these are how much lighter than LH 2.4 dog dish? Also you can run what a smaller clutch? is that It, sorry my mind forgot this stuff. 8.5" instead of 9" ?

This a stock Volvo flywheel as used in the 240 KJets and non-turbo 240 LH2.2. It's not going to shatter as it hasn't been lightened appreciably other than reduce the diameter perhaps .125 inches and some dimples around the circumference. Yup, they take an 8.5" setup. I think I read they are around 10 pounds lighter. But...I did this out of neccessity. There are no dog dish sensor flywheels to be had locally. And, if I was going to have to mod a 2.2 dog dish....why not a flat one and save some weight.

swiftjustice44 said:

This a stock Volvo flywheel as used in the 240 KJets and non-turbo 240 LH2.2. It's not going to shatter as it hasn't been lightened appreciably other than reduce the diameter perhaps .125 inches and some dimples around the circumference. Yup, they take an 8.5" setup. I think I read they are around 10 pounds lighter. But...I did this out of neccessity. There are no dog dish sensor flywheels to be had locally. And, if I was going to have to mod a 2.2 dog dish....why not a flat one and save some weight.

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wish I had thought of that...I went LH2.2 and would have rather have LH2.4 on my conversion....oh well

good job !!!

What's cool is any 8 bolt Volvo flat flywheel can be used. Cheap!

That's ****ing clever as hell. I'll have to remember that.

Good job. James (945ti) did the same thing to a flat flywheel a couple years ago but I'm not sure if he ever ended up using it.

crazy0000 said:

So no foot severances yet! fingers crossed. Pardon my ignorance, I know I should know this, but these are how much lighter than LH 2.4 dog dish? Also you can run what a smaller clutch? is that It, sorry my mind forgot this stuff. 8.5" instead of 9" ?

Click to expand...

swiftjustice44 said:

This a stock Volvo flywheel as used in the 240 KJets and non-turbo 240 LH2.2. It's not going to shatter as it hasn't been lightened appreciably other than reduce the diameter perhaps .125 inches and some dimples around the circumference. Yup, they take an 8.5" setup. I think I read they are around 10 pounds lighter. But...I did this out of neccessity. There are no dog dish sensor flywheels to be had locally. And, if I was going to have to mod a 2.2 dog dish....why not a flat one and save some weight.

Click to expand...

To help dispel fears of 'foot severance' and 'shattering flywheels' once significant lightening has been done properly, it can be noted that Volvo's 'Competition Service' itself offered these stock, 21-22 lbs flywheels lightened to 18 lbs for the 6-bolt B18/B20 engines.

When said 'Competition Service' was renamed 'R-Sport', at the time when Volvo formally entered into racing, the same stock flywheels were lightened into a 16 lbs version. Volvo's part-numbers for the latter are:

- 419392-6 for the 6-bolt B18/B20
- 552833-6 for the 8-bolt B20/B21/B23

'Swiftjustice', does it look like the crank-sensor could be moved another 5/8'' inward so as to eventually 'read' a lightened flywheel, like the one in the following link, if it was modified for LH2.4? :

http://forums.turbobricks.com/showthread.php?t=154762

I don't presently have a RWD LH2.4 flexplate at hand to verify wether replicating the 'trigger-dimples' into that lightened flywheel would interfere with it's bolt-holes for clutch-cover installation.

If I learn that the LH2.4 crank-sensor could be positioned to 'read' such an eventual set-up, though, I will definitely look further into the possibilty of modifying that lightened flywheel accordingly.

Thanks.

Well, as long as the dead spot stays relative to the bolt pattern it should not be difficult. I'm no mathmatician, but if there's 60 equal positions on a circle that comes out pretty close to 6 degrees per mark. Your flywheel's diameter is appreciably smaller so the markings will be closer together. A flexplate could still be used to check your reference marks prior to drilling. Without benefit of better equipment, I'd have to make the original points with compass and protractor. Not drilling into pressure plate mountings would indeed be an issue for you; I'd mock it up and see. As for getting the sensor close enough I suspect one may need to McGyver it...I don't think the o.e. bracket would work but the crank sensor doesn't really care where it is so long as it is close enough to register. Remember folks, these are dimples not holes. I didn't drill to China...3/8 in max depth and a 3/8" bit which fits exactly thru the sensor ring of the flexplate. I'm no clutch guru, I didn't do this to run the Big Bend Open Road Race. I did this out of desperartion. LH2.4 flywheels in Dallas are still on the car at j/y's. When they pull the motors, the flywheel goes with it. No one would deliver only a flywheel and I had no way to leave the shop so....I could either order a used motor and swap the flywheel for my flexplate and send the motor back (risky) or give this a shot. Nice to know it works.

You could always just flatten the 2.4 wheel.

How much does yours weigh?

Well, I didn't do anything to the back side and the thickness looks very similar to yours. Didn't bother to weigh it. Maybe a little less than yours as diameter has been reduced a hair. Would have been more than happy to turn a 2.4 flywheel down. The thread starts out with me mentioning the difficulty of finding them here in the Dallas area. Flat 8 bolt flywheels from n/a and pre 84.5 turbo 240s are quite common. The one 2.4 flywheel I found, the guy wanted $150 for it and it had bad hot spots. All I was trying to do is get my car back on the road without paying an arm and a leg; the performance end of it is just a nice side effect. The car has a squirter block with 800 miles on a total rebuild. Large NPR, T3/T4, 012 amm, 3" plumbing, 4 bar, Stratmoshere adjustable CBV, 75# injectors and Mike's chips. Really not looking for decreased mass and less inertia, blah blah blah. The car is plenty quick; for anything serious there's always my V8.

Now you just have to contend with tranny explodish. Great work and thanks for also detail the bit and depth used. Be interested to see if it behaves different at high rpms. I wouldn't think so as it looks alot like the 2.4 dog dish as far as holes go.

Thanks

What are you going to do about the cutout for the crank sensor that the M46 dosn't have?

Gone to the j/y to try this today

WrenWright said:

What are you going to do about the cutout for the crank sensor that the M46 dosn't have?

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Every M46 I've seen has the outline for the cut out; even the 84 tranny I'm installing. The bell housing is real thin at that area and from inside you can see the outline where the sensor would go...today I took a cut off wheel and removed the excess and used a die grinder to finish it out. I sppose I could have swapped bell housings but cutting it out was simple w/ air tools. Took me about 15 minutes.










And, yeah, I don't expect these transmissions to last too long. A T5 is the minimum for the torque I'm making. But, at least I'll have the pita of installing the clutch/brake out of the way. I just need it back on the road so I can get back to finishing my 144.